Calcium carbonate is an effective phosphorus binder in children with chronic renal failure

Management of acute kidney injury in children: a guide for pediatricians

Acute kidney injury (AKI; previously called acute renal failure) is characterized by a usually reversible increase in the blood concentration of creatinine and nitrogenous waste products and by the inability of the kidney to appropriately regulate fluid and electrolyte homeostasis. The incidence of AKI in children appears to be increasing and the etiology of AKI over the past decades has shifted from primary renal disease to multifactorial causes, particularly in hospitalized children. Renal failure can be divided into prerenal failure, intrinsic renal disease including vascular insults, and obstructive uropathies. The history, physical examination, and laboratory studies including a urinalysis and radiographic studies can establish the likely cause(s) of AKI. Once intrinsic renal failure has become established, management of the metabolic complications of AKI requires meticulous attention to fluid balance, electrolyte status, acid-base balance, and nutrition. Many children with AKI will need renal replacement therapy to remove endogenous and exogenous toxins and to maintain fluid, electrolyte, and acid-base balance until renal function improves. Renal replacement therapy may be provided by peritoneal dialysis (PD), intermittent hemodialysis (HD), or hemofiltration with or without a dialysis circuit. Many factors--including the age and size of the child, the cause of renal failure, the degree of metabolic derangements, blood pressure, and nutritional needs--are considered in deciding when to initiate renal replacement therapy and which modality of therapy to use. The prognosis of AKI is highly dependent on the underlying etiology of the AKI. Children who have AKI as a component of multisystem failure have a much higher mortality rate than children with intrinsic renal disease. Recovery from intrinsic renal disease is also highly dependent on the underlying etiology of the AKI. Children who have experienced AKI from any cause are at risk for late development of renal failure long after the initial insult. Such children need life-long monitoring of their renal function, blood pressure, and urinalysis.

Chronic kidney disease mineral and bone disorder in children

Childhood and adolescence are crucial times for the development of a healthy skeletal and cardiovascular system. Disordered mineral and bone metabolism accompany chronic kidney disease (CKD) and present significant obstacles to optimal bone strength, final adult height, and cardiovascular health. Decreased activity of renal 1 alpha hydroxylase results in decreased intestinal calcium absorption, increased serum parathyroid hormone levels, and high-turnover renal osteodystrophy, with subsequent growth failure. Simultaneously, phosphorus retention exacerbates secondary hyperparathyroidism, and elevated levels contribute to cardiovascular disease. Treatment of hyperphosphatemia and secondary hyperparathyroidism improves growth and high-turnover bone disease. However, target ranges for serum calcium, phosphorus, and parathyroid hormone (PTH) levels vary according to stage of CKD. Since over-treatment may result in adynamic bone disease, growth failure, hypercalcemia, and progression of cardiovascular calcifications, therapy must be carefully adjusted to maintain optimal serum biochemical parameters according to stage of CKD. Newer therapeutic agents, including calcium-free phosphate binding agents and new vitamin D analogues, effectively suppress serum PTH levels while limiting intestinal calcium absorption and may provide future therapeutic alternatives for children with CKD.

PHOSPHORUS METABOLISM AND MANAGEMENT IN CHRONIC KIDNEY DISEASE: Renal Osteodystrophy, Phosphate Homeostasis, and Vascular Calcification

New advances in the pathogenesis of renal osteodystrophy (ROD) change the perspective from which many of its features and treatment are viewed. Calcium, phosphate, parathyroid hormone (PTH), and vitamin D have been shown to be important determinants of survival associated with kidney diseases. Now ROD dependent and independent of these factors is linked to survival more than just skeletal frailty. This review focuses on recent discoveries that renal injury impairs skeletal anabolism decreasing the osteoblast compartment of the skeleton and consequent bone formation. This discovery and the discovery that PTH regulates the hematopoietic stem cell niche alters our view of secondary hyperparathyroidism in chronic kidney disease (CKD) from that of a disease to that of a necessary adaptation to renal injury that goes awry. Furthermore, ROD is shown to be an underappreciated factor in the level of the serum phosphorus in CKD. The discovery and the elucidation of the mechanism of hyperphosphatemia as a cardiovascular risk in CKD change the view of ROD. It is now recognized as more than a skeletal disorder, it is an important component of the mortality of CKD that can be treated.

Secondary hyperparathyroidism in children with chronic renal failure: pathogenesis and treatment

Despite advances in the management of patients with chronic renal failure, histologic features associated with secondary hyperparathyroidism remain the predominant skeletal findings; however, over the last decade the prevalence of adynamic bone has increased in both adult and pediatric patients with chronic renal failure. The management of children with secondary hyperparathyroidism and mild to moderate chronic renal failure should be started early, and should include correction of hypocalcemia and metabolic acidosis, maintenance of age-appropriate serum phosphorus levels, and institution of vitamin D therapy when serum intact parathyroid hormone (PTH) measurements are elevated to maintain the blood levels within normal limits; however, in children undergoing chronic dialysis therapy, the current recommendation is to maintain the serum intact PTH levels at least 2-4 times the upper limits of normal to prevent the development of low bone turnover disease. Serum calcium, phosphorus, alkaline phosphatase, and PTH levels should be monitored frequently, especially in infants and very young children. Discontinuation or reduction of vitamin D should be considered when there is a rapid decline in PTH levels, persistent elevation in serum calcium and serum phosphorus levels, and a significant diminution in alkaline phosphatase levels. In addition, a reduction in the calcium concentration of the dialysis fluid, and judicious use of calcium-containing salts as phosphate binding agents should also be performed in these patients. Although not yet extensively used in pediatric patients with secondary hyperparathyroidism, several therapeutic alternatives, such as the less calcemic vitamin D analogs, including paricalcitol [19-nor-1,25-(OH)(2)D(2)] and doxercalciferol [1-alpha-(OH)(2)D(2)], calcimimetics, and the availability of a calcium-free, aluminum-free phosphate binder such as sevelamer hydrochloride and lanthanum carbonate, may play significant roles in the future management of children with secondary hyperparathyroidism to promote linear growth, prevent parathyroid gland hyperplasia, avoid calciphylaxis and, in the long run, avert vascular calcifications.

Acute renal failure in the newborn

Acute renal failure in the newborn is a common problem and is typically classified as prerenal, intrinsic renal disease including vascular insults, and obstructive uropathy. In the newborn, renal failure may have a prenatal onset in congenital diseases such as renal dysplasia with or without obstructive uropathy and in genetic diseases such as autosomal recessive polycystic kidney disease. Acute renal failure in the newborn is also commonly acquired in the postnatal period because of hypoxic ischemic injury and toxic insults. Nephrotoxic acute renal failure in newborns is usually associated with aminoglycoside antibiotics and nonsteroidal anti-inflammatory medications used to close a patent ductus arteriosis. Alterations in renal function occur in approximately 40% of premature newborns who have received indomethacin and such alterations are usually reversible. Renal artery thrombosis and renal vein thrombosis will result in renal failure if bilateral or if either occurs in a solitary kidney. Cortical necrosis is associated with hypoxic/ischemic insults due to perinatal anoxia, placenta abruption and twin-twin or twin-maternal transfusions with resultant activation of the coagulation cascade. As in older children, hospital acquired acute renal failure is newborns is frequently multifactorial in origin. Although the precise incidence and prevalence of acute renal failure in the newborn is unknown, several studies have shown that acute renal failure is common in the neonatal intensive care unit. Recent interesting studies have demonstrated that some newborns may have genetic risks factors for acute renal failure. Once intrinsic renal failure has become established, management of the metabolic complications of acute renal failure continues to involve appropriate management of fluid balance, electrolyte status, acid-base balance, nutrition and the initiation of renal replacement therapy when appropriate. Renal replacement therapy may be provided by peritoneal dialysis, intermittent hemodialysis, or hemofiltration with or without a dialysis circuit. The preferential use of hemofiltration by pediatric nephrologists is increasing while the use of peritoneal dialysis is decreasing except for neonates and small infants. Peritoneal dialysis has been a major modality of therapy for acute renal failure in the neonate when vascular access may be difficult to maintain. In the newborn, the prognosis and recovery from acute renal failure is highly dependent upon the underlying etiology of the acute renal failure. Factors that are associated with mortality include multiorgan failure, hypotension, need for pressors, hemodynamic instability, and need for mechanical ventilation and dialysis. The mortality and morbidity of newborns with acute renal failure is much worse in neonates with multiorgan failure. Newborns who have suffered substantial loss of nephrons as may occur in cortical necrosis are at risk for late development of renal failure after apparent recovery from the initial insult. Similarly, hypoxic/ischemic and nephrotoxic injury to the developing kidney can result is decreased nephron number. Newborns with acute renal failure need life-long monitoring of their renal function, blood pressure, and urinalysis. Typically, the late development of chronic renal failure will first becomes apparent with the development of hypertension, proteinuria, and eventually an elevated blood urea nitrogen and creatinine.

Safety of New Phosphate Binders for Chronic Renal Failure

Phosphate (Pi) retention is a common problem in patients with chronic kidney disease, particularly in those who have reached end-stage renal disease (ESRD). In addition to causing secondary hyperparathyroidism and renal osteodystrophy, recent evidence suggests that, in ESRD patients, high serum phosphorus concentration and increased calcium and phosphorous (Ca x P) product are associated with vascular and cardiac calcifications and increased mortality. Dietary phosphorus restriction and Pi removal by dialysis are not sufficient to restore Pi homeostasis. Reduction of intestinal Pi absorption with the use of Pi binders is currently the primary treatment for Pi retention in patients with ESRD. The use of large doses of calcium-containing Pi binders along with calcitriol administration may contribute to over-suppression of parathyroid hormone secretion and adynamic bone disease as well as to a high incidence of vascular calcifications. When used in patients with impaired renal function, aluminium salts were found to accumulate in bone and other tissues, resulting in osteomalacia and encephalopathy.Sevelamer, an aluminium- and calcium-free Pi binder can reduce serum phosphorus concentration and is associated with a significantly lower incidence of hypercalcaemia, while maintaining the ability to suppress parathyroid hormone production. An additional benefit of sevelamer is its ability to lower low density lipoprotein-cholesterol and total cholesterol levels. Sevelamer attenuates the progression of vascular calcifications in haemodialysis patients, which may lead to lower mortality. The use of sevelamer in non-dialysed patients might aggravate metabolic acidosis, common in these patients. Several other calcium-free Pi binders are in development. Lanthanum carbonate has shown significant promise in clinical trials in ESRD patients. Magnesium salts do not offer a significant advantage over currently available Pi binders. Their use is restricted to patients receiving dialysis since excess magnesium must be removed by dialysis. Iron-based compounds have shown variable efficacy in short-term clinical trials in small numbers of haemodialysis patients. Mixed metal hydroxyl carbonate compounds have shown efficacy in animals but have not been studied in humans. Major safety issues include absorption of the metal component with possible tissue accumulation and toxicity.

Calcium acetate versus calcium carbonate as oral phosphate binder in pediatric and adolescent hemodialysis patients

Calcium carbonate is widely used as an oral phosphorus binder to control hyperphosphatemia in children on maintenance hemodialysis. Intestinal calcium absorption may induce hypercalcemia, particularly if calcitriol is given simultaneously. In adults, calcium acetate binds phosphorus more effectively than calcium carbonate, while reducing the frequency of hypercalcemic events. We therefore compared calcium acetate with calcium carbonate in nine pediatric patients on long-term maintenance hemodialysis. Following a 1-week withdrawal of phosphorus binders, calcium carbonate was administered for 7 weeks; after a second withdrawal, calcium acetate was given for another 7 weeks. All patients received calcitriol regularly. Both agents lowered the serum phosphorus concentration significantly (calcium carbonate 5.7 +/- 1.4 vs. 7.7 +/- 2.1 mg/ dl, P < 0.005; calcium acetate 5.8 +/- 1.4 vs. 7.8 +/- 2.0 mg/dl, P < 0.005). Significantly less elementary calcium was ingested with calcium acetate than with calcium carbonate: 750 (375-1,500) vs. 1,200 (0-3,000) mg calcium/day, P < 0.0001. Wit calcium carbonate serum calcium increased significantly. The number of episodes of hyperphosphatemia or hypercalcemia did not differ between treatments. Intact plasma parathyroid hormone (PTH) decreased significantly with both phosphate binders, and serum 25-hydroxyvitamin D3 increased. There was a close relationship between serum phosphorus and PTH in prepubertal but not in pubertal patients. We conclude that hyperphosphatemia can be controlled effectively by both calcium acetate and calcium carbonate in pediatric hemodialysis patients. The oral load of elementary calcium is reduced significantly by binding phosphorus with calcium acetate instead of calcium carbonate; nevertheless, hypercalcemic episodes remain equally frequent with both phosphate binders.

Calcium mass transfer with dialysate containing 1.25 and 1.75 mmol/L calcium in peritoneal dialysis patients

Studies with 1.75 mmol/L calcium dialysate have shown that patients gain calcium from dialysate. Thus, hypercalcemia, especially when calcium compounds are used for phosphate control, is a commonly seen complication. Dialysate with 1.25 mmol/L calcium has been available since 1989. Little is known about calcium mass transfer (CMT) with dialysate of this calcium concentration. CMT was measured in 20 stable adult peritoneal dialysis patients. Each CMT study consisted of a 2-L continuous ambulatory peritoneal dialysis (CAPD) exchange with a dwell time of 4 hours. CMT studies were performed using 1.25 and 1.75 mmol/L calcium dialysate with 1.5, 2.5, and 4.25 g/dL dextrose concentrations. CMT with 1.25 mmol/L calcium dialysate was compared to that with 1.75 mmol/L for each dextrose concentration. With a dextrose concentration of 1.5 g/dL, the mean CMT for 1.25 mmol/L calcium dialysate was -0.1 +/- 0.3 mmol versus 0.6 +/- 0.3 mmol for 1.75 mmol/L calcium dialysate (P < 0.0001). A dextrose concentration of 2.5 g/dL resulted in a mean CMT of -0.4 +/- 0.2 mmol for 1.25 mmol/L calcium versus 0.45 +/- 0.25 mmol for 1.75 mmol/L calcium (P < 0.0001). Using a dextrose concentration of 4.25 g/dL, the mean CMT was -0.7 +/- 0.25 mmol for 1.25 mmol/L calcium versus -0.05 +/- 0.35 mmol for 1.75 mmol/L calcium (P < 0.0001). Mean serum ionized calcium (SiCa) was between 1.15 and 1.20 mmol/L for all study groups. CMT inversely correlated with SiCa for each type of dialysate used. CMT was dependent on the concentrations of calcium and dextrose in the dialysate and the SiCa level at the time of the exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of vitamin D-binding protein and vitamin D metabolite loss in children on continuous ambulatory peritoneal dialysis

We measured the serum concentration of vitamin D-binding protein (DBP) in children with chronic renal failure (CRF). We also evaluated the relationships between the peritoneal loss of vitamin D metabolites, DBP and albumin in nine children on continuous ambulatory peritoneal dialysis (CAPD). The serum levels of DBP in children with CRF were significantly higher than in normal children. The mean serum DBP level in CRF children undergoing CAPD was slightly lower than in CRF patients who were not on dialysis. In patients on CAPD, the peritoneal loss of 25-hydroxyvitamin D (25OHD) showed a significant positive correlation with the DBP concentration in the dialysate (r = 0.855, P less than 0.005). In contrast, the peritoneal loss of 1,25-dihydroxyvitamin D (1,25(OH)2D) showed a significant correlation with the loss of albumin in the dialysate (r = 0.779, P less than 0.01). The synthesis of 1,25(OH)2D3 is reduced in advanced renal failure, and the peritoneal losses of the active vitamin D sterols in patients on CAPD may aggravate this deficiency. We recommend that supplementation of active form of vitamin D, such as 1 alpha-hydroxyvitamin D3 or 1,25(OH)2D3, is important in CAPD patients, particularly those with elevated peritoneal loss of DBP and/or albumin.

Etiology of hypercalcemia in hemodialysis patients on calcium carbonate therapy

Fourteen of 39 dialysis patients (36%) became hypercalcemic after switching to calcium carbonate as their principal phosphate binder. In order to identify risk factors associated with the development of hypercalcemia, indirect parameters of intestinal calcium reabsorption and bone turnover rate in these 14 patients were compared with results in 14 eucalcemic patients matched for age, sex, length of time on dialysis, and etiology of renal disease. In addition to experiencing hypercalcemic episodes with peak calcium values of 2.7 to 3.8 mmol/L (10.7 to 15.0 mg/dL), patients in the hypercalcemic group exhibited a significant increase in the mean calcium concentration obtained during 6 months before the switch, compared with the mean value obtained during the 7 months of observation after the switch (2.4 +/- 0.03 to 2.5 +/- 0.03 mmol/L [9.7 +/- 0.2 to 10.2 +/- 0.1 mg/dL], P = 0.006). In contrast, eucalcemic patients exhibited no change in mean calcium values over the same time period (2.3 +/- 0.05 to 2.3 +/- 0.05 mmol/L [9.2 +/- 0.2 to 9.2 +/- 0.2 mg/dL]). CaCO3 dosage, calculated dietary calcium intake, and circulating levels of vitamin D metabolites were similar in both groups. Physical activity index and predialysis serum bicarbonate levels also were similar in both groups. However, there was a significant difference in parameters reflecting bone turnover rates between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal osteodystrophy in patients on continuous ambulatory peritoneal dialysis

Twelve patients on continuous ambulatory peritoneal dialysis (CAPD) were studied in order to evaluate the progression of renal osteodystrophy (ROD). All patients received doses of 0.01-0.02 microgram/kg of 1 alpha vitamin D3 (1 alpha-D3) and 0.1-0.15 g/kg of calcium carbonate for 12-18 months. Serum total protein, total calcium (Ca), creatinine, inorganic phosphate, alkaline phosphatase (ALP), and n-terminal parathyroid hormone were measured regularly. The radiological bone appearance for ROD or rickets and the height standard deviation score were compared between the outset and the end of this study. An increase of Ca values and a decrease of ALP values correlated with a suppression of hyperparathyroidism, and the hyperphosphatemia was controlled in the majority of our patients throughout this study. Two patients had ROD and rickets at the outset of this study, and all patients but one had neither ROD nor rickets at the end of this study. Growth retardation improved or remained stable in 10 patients. Our results indicate that adequate doses of 1 alpha-D3 and calcium carbonate are effective in the prevention of ROD and rickets in patients on CAPD.

Calcium acetate, an effective phosphorus binder in patients with renal failure

Calcium salts are increasingly used as phosphorus binders in patients with chronic renal failure. Calcium carbonate is the principal salt presently utilized, however, other calcium salts may be more effective and safer phosphorus binders. Theoretical calculations, in vitro experiments, and in vivo studies in normal subjects have shown calcium acetate to be a more effective phosphorus binder than other calcium salts. This salt has not previously been studied in patients with chronic renal failure. We used a one-meal gastrointestinal balance technique to measure phosphorus absorption, calcium absorption and phosphorus binding in six patients with chronic renal failure. Calcium acetate was compared with calcium carbonate and placebo. Equivalent doses (50 mEq Ca++) of calcium acetate bound more than twice as much phosphorus (106 +/- 23 mg) as calcium carbonate (43 +/- 39 mg) P less than 0.05. When phosphorus binding was factored for calcium absorption, calcium acetate bound 0.44 mEq HPO4 =/mEq absorbed Ca++ compared with 0.16 mEq HPO4 = bound/mEq Ca++ absorbed with calcium carbonate. More efficient phosphorus binding permits serum phosphorus concentration to be controlled with lower doses of calcium salts. The higher phosphorus binding/calcium absorption ratio coupled with a lower dose indicates that less calcium will be absorbed when calcium acetate is used for phosphorus control. Markedly positive calcium balance, hypercalcemia and ectopic calcification should be less likely to occur with this drug than other calcium salts.

Recent developments in aluminum toxicology

Aluminum is now recognised as an important toxin causing considerable morbidity and mortality, particularly in patients with chronic renal failure. Diseases that have been associated with aluminium include dialysis dementia, renal osteodystrophy and Alzheimer's disease. Aluminum also has an effect on red blood cells, parathyroid glands and chromosomes. Accumulation of aluminium in the body tends to occur when the gastrointestinal barrier is circumvented. This has been identified as a problem during dialysis or intravenous fluid administration. Renal functional impairment results in decreased aluminum excretion and promotes accumulation of the element in the body. Many sources have been shown to be contaminated with aluminium. These include the water used for dialysis; medicines containing aluminium, such as aluminium-containing phosphate binding gels; total parenteral nutrition solutions; processed human serum albumin; intravenous fluids in infants; and other environmental and industrial sources. The management of aluminium toxicity involves the identification of these contaminated sources and subsequent removal of the element. This includes regular monitoring of water used in dialysis. The use of aluminium-containing phosphate binding gels in patients with compromised renal function should be reviewed and alternatives sought. The development of effective aluminium-free phosphate binders is desirable. Once a patient has aluminium toxicity, desferrioxamine (deferoxamine) has been shown to be an effective agent in its chelation and removal.

Reduction of dietary phosphorus absorption by phosphorus binders. A theoretical, in vitro, and in vivo study

Antacids used to decrease phosphorus absorption in patients with renal failure may be toxic. To find more efficient or less toxic binders, a three-part study was conducted. First, theoretical calculations showed that phosphorus binding occurs in the following order of avidity: Al3+ greater than H+ greater than Ca2+ greater than Mg2+. In the presence of acid (as in the stomach), aluminum can therefore bind phosphorus better than calcium or magnesium. Second, in vitro studies showed that the time required to reach equilibrium varied from 10 min to 3 wk among different compounds, depending upon solubility in acid and neutral solutions. Third, the relative order of effectiveness of binders in vivo was accurately predicted from theoretical and in vitro results; specifically, calcium acetate and aluminum carbonate gel were superior to calcium carbonate or calcium citrate in inhibiting dietary phosphorus absorption in normal subjects. We concluded that: (a) inhibition of phosphorus absorption by binders involves a complex interplay between chemical reactions and ion transport processes in the stomach and small intestine; (b) theoretical and in vitro studies can identify potentially better in vivo phosphorus binders; and (c) calcium acetate, not previously used for medical purposes, is approximately as efficient as aluminum carbonate gel and more efficient as a phosphorus binder than other currently used calcium salts.

Treatment of severe hypercalcemia with peritoneal dialysis in an infant with end-stage renal disease

Recurrent and unusually severe hypercalcemia was observed in an infant undergoing continuous cycling peritoneal dialysis and receiving oral calcitriol and calcium carbonate. Rapid correction was achieved with peritoneal dialysis using a calcium-free dialysis solution.